Camera movement and dolly zoom with Chronos high-speed camera-----make money online

today on Applied Science I'm going to

talk about the Kronos high speed camera

mounted to this motorized linear rail so

I move the camera very quickly while

something is happening here and get a

dynamic high-speed video shot so here's

an example of the type of footage that

it creates and just like with

conventional video having camera

movement makes the shot more exciting

and more engaging so think of like Blair

Witch Project versus you know a

documentary clearly having a camera

movements or it gives it that extra

punch and even though high-speed video

is pretty awesome in its own with the

camera movement it gives you that extra

little bit of push that makes the shot

more interesting after that I'm going to

show you some clips of my favorite high

speed footage not necessarily collected

with the rail and then we'll talk about

the dolly zoom technique in high speed

using this rig so let's take a look at

some of the details with this here's a

look at the drive side of this linear

actuator system and I have it set for a

slow speed so you can see it in action

here these things can be pretty tricky

to find even if you have the budget I

haven't found a source of new linear

actuators like this that's easy to use

it's pretty much all high-touch sales

and then after you get through all that

it is a very high price so pretty much

eBay is your main option for these and

that's a that's where I got this one so

keep in mind that when your actuators

fall into two main categories you've got

sort of like the screw screw actuator

mechanisms where this is turned by the

motor this way and the thread the pitch

of the screw is actually what drives the

carriage back and forth and this is fine

for low speed and high precision

applications like a CNC machine but for

this we want the camera moving really

quickly so inside here there's actually

a belt that goes in this direction and

is turned by a cog wheel that's

connected to the motor over here so for

every revolution of the COG wheel the

belt moves one circumference of the of

the COG wheel so in this case the

diameter of the wheel here is maybe 25

millimeters so you get about pi times

that for every revolution and then if

you know how fast your motor goes you

can figure out what the top speed of

your linear carriage is going to be

in this case the stepper motor that came

with this linear drive system just

wasn't powerful enough or fast enough in

fact there was even a sticker on this

that said maximum speed 42 inches per

second which young going much faster

than that but my justification was that

that was at full load this thing is

rated to carry like a hundred pounds or

something like that so it's just the

camera on here I figure I can go a lot

faster so I cut the stepper motor mount

off and then made this aluminum bracket

and mounted to it this Technic servo

motor a clear path and this is the same

motor that I was using in my previous

video where I was whipping the camera

around on a rotary rig keep in mind that

if you have a system where you have sort

of two bearings holding a shaft here so

this motor has a bearing here and here

and inside the linear rail those are

bearing here and here so the two shafts

are completely fixed relative and there

could be some misalignment in fact

there's going to be some misalignment so

you have to use a shaft coupler in this

case and I'm really fond of these shaft

couplers from McMaster that clamped down

on the shaft instead of using a set

screw they're quite nice and they also

account for axial misalignment so simple

shaft couplers will allow you to have an

angular misalignment but in this case

since there's barrett two sets of

bearings we have to account for the fact

that the shafts might be offset like

this and in that case you need a coupler

that has sort of two flex points to

allow that to work initially i thought i

was going to need a rigid mounting

bracket to attach the camera to the

moving part of the axis here i was

worried that the acceleration forces

were going to be too much and they turn

out to be you know in the range of like

1 to 5g which sounds like a lot but if

you think about just carrying a camera

in your hands and just kind of swinging

it around just sort of normally to get a

shot of a moving animal or something

like that it's actually in the same

range 1 to 5 g that you can move it

around with your hands so the amount of

flexibility that you get hardy-har if

you put a flex joint like this ball and

socket joint between the moving part in

the camera it makes it so much easier to

frame the shot that it's completely

worth it and this this thing with stands

the 1 to 5 g no problem this is actually

a speaker wall mount bracket

and I'll put the links to all this stuff

in the description so initially I made

that first clip of the water being

splashed with just the the ball joint

attached to the axis and moving it

linearly across so it's called a truck

shot in film terminology I guess because

your camera would be on a truck that

rolls along on rails side to side

panning is when you take the camera and

angle it back and forth but truck is

when you move it side to side in a

straight line so I thought that was all

well and good but the next advancement

was to keep the action in the shot a

little bit longer and so ideally what I

wanted was to have the camera facing the

action with this sort of dynamic you

know excitement that you get from camera

movement and then you know moving past

the action that's staying in view more

so I came up with this rig this is a

bearing under here attached to a

lightweight fiberglass rod and then

there's another bearing on this side of

the table that's sticked down to the

table with double stick tape so now if

we actuate it

you can see that the camera always faces

that one spot so what we can do is put

our subject of interest right above the

pivot point there and then the camera

will always follow it I'm using an 8

millimeter lens which has a couple

benefits one the 8 millimeter lens is a

lot smaller so we can whip the camera

around faster and not have quite as much

you know jostling and stuff and also it

gives it easier framing so you know

we're pretty close to the action eight

millimeters works out pretty well

I haven't yet collected a lot of footage

with this setup yet so please leave

suggestions in the comments here's a

look at the servo control software you

can configure this thing to be in many

modes like for example you can feed the

servo a PWM signal and have that

translated to velocity but currently I

have this set up to just go to different

pre-programmed positions and so it's

meant to sort of download the

configuration over USB into the motor

and then you can disconnect it and just

use those raw digital inputs to control

the motors position however you can

override the inputs and then control the

entire thing through USB so what I've

been doing to collect all of my footage

is just hover the mouse cursor over this

box and then if I pick the mouse up off

the desk I can just click the left mouse

button and it will you know cause the

motor to move so it's a super easy way

for me to just walk around the room with

the mouse and at the right time I can

you know sequence the shot so that I can

you know drop the ball into the water

and then click this at just the right

time so it's very configurable I have it

set up going very slowly now you can

give an overall speed limit you can give

an acceleration limit and it even has a

jerk limit so if you haven't heard of

this just like how acceleration is the

change in velocity over time jerk is the

change in acceleration over time so if

you're you know imagine you're in your

car and you're coming to a stoplight

if you don't ease off the brake just

before the car comes to a stop you feel

the car jerk right like that that's

where it comes from and in automation

systems like this jerk is what causes

lots

of sort of banging and O's on motor

startup so this thing has a way to limit

the jerk basically also it has this

oscilloscope function which is quite

useful you can plot all kinds of

different variables in here so commanded

motor torque will just make this run

again so you can see the torque is a

little bit higher when we started moving

and then levels off to this steady state

as it's going so let's turn the speed

limit up up to 2,000 rpm so this this is

about two and a half meters per second

linear travel and you can hear it in the

background it's moving a lot faster now

so we'll take another run and

surprisingly it didn't actually use that

much torque it was applied for a little

bit longer this is full scale so this is

100% torque and this is about 25% of the

motors available torque so let's try

plotting actual velocity and do another

run so what's interesting here is that

it's the motor is accelerating because

the velocity is going up and then it

smoothly crests and comes back down and

it's not quite making it to 2,000 rpm

which is this line here and the reasons

that our acceleration limit is

preventing the motor from ever getting

up to full speed so what we can do is

make the acceleration limit higher

12,000 rpm per second and we'll have a

run you can hear it sounds much more

aggressive now and now what's happening

is the acceleration causes this slope to

be higher and now it's actually peaking

and hitting the speed limit here so this

software is really nice for programming

the motion and these these positions up

here are the actual physical locations

since it knows where it's going and

where it's starting from it can plot the

planner can sort of make this motion

profile the servo motor also has a

digital output that you can program to

be many things it's actually very high

level so this thing is intended to be

used for example in industrial

automation settings and you can set up

the digital output to change state when

the motor gets to where

intending to go so for example you can

command the motor to go somewhere and

then you know it'll be moving and then

when it gets to its destination it will

signal that it's done so if you have

this thing in a sequence of events it's

very easy to sort of set this up without

a lot of programming or really any

programming one downside is that the

digital output does not give you like a

it doesn't give you the raw shaft

encoder output and you can't program it

to give you any sort of position

information you can have a PWM output so

if you want to know how fast the motor

is going it will tell you it will give

you a digital PWM signal out but like I

say it doesn't give you actual position

which is a big problem for this next

thing we're going to talk about but

first let's take a look at some of my

favorite high speed video clips that

I've collected over the past month

[Music]

[Music]

okay so the last thing I wanted to talk

about was the dolly zoom technique so we

mentioned that truck is when you move

the lens side-to-side and panning is

when you turn it side to side dolly is

when you move the lens and camera toward

and away from the subject and you know

what zooming is zooming is just changing

the focal length that your lens like

this so if you combine the focal length

change and the movement it's called

dolly zoom and this is what it looks

like so as you can see the idea is that

the subject stays about the same size

within the frame but the perspective

changes and so if you compare the

subject to the background you notice

there's a lot of sort of you know

perceived movement there and this

technique was made popular in the movie

vertigo showed up in Jaws it's actually

used here and there and usually it's

used when a character is having like a

terrible realization because the effect

is so unsettling and so someone in the

comments of my last video said hey now

that you have this high-speed linear

rail you should do a dolly zoom in

high-speed and I thought that was a

fantastic suggestion so the trick here

is that we need another position

controlled motor to adjust the focal

length of the lens as this cameras in

motion and to do that I used another

servo motor a much smaller servo motor

this is the Mehcad we know and so here's

the setup showing the motor coupled to

the camera and in fact this is a

Kickstarter bolted to a Kickstarter

Mehcad we know was successfully funded a

while back and Chronos was as well and

the nice thing about this is that the

code running on this small servo motor

is it's in the Arduino IDE and it's open

source and even better than that there

is a microcontroller with analog inputs

on the board so what I did is I added a

10 turn potentiometer and then bolted

this to the moving part of the linear

axis to determine where it was on the a

rail so I mentioned unfortunately

there's no step output from the motor

controller that's driving the linear

rail otherwise I would have just tapped

into that and used that and I also

thought of other ways that I could

couple the

the smaller servomotor into the bigger

one you know through other shaft

encoders or whatever

this solution ended up working out okay

it wasn't great obviously one of the

biggest problems is that this wheel will

slip and so as it goes along back and

forth a number of times after setting up

the shot eventually this thing won't be

in the right spot anymore so you may

have noticed in the footage that I

showed earlier there's a problem the

camera actually goes out of focus so

this this is sort of working the way

it's supposed to so imagine you how to

zoom lens and you were you know taking a

video of a bird or something if you

zoomed in on the bird you would want it

to stay in focus meaning that if you

change the focal length of the lens you

still want it to be in focus when you

get to the new focal length and that

property is called being parfocal so

most lenses are set up to do this either

digitally or through up or through the

optical design but for this dolly zoom

technique we're going to be moving the

lens toward the subjects or our focal

distance is changing at the same time so

to do this right you would actually need

two motors one to change the focal

length and another one to change the

focus ring because we actually are

moving closer to the subject so this

doubles the complexity of the project

and introduces a whole bunch of other

source of problems and whatnot but

there's an easy way to get out of this

we can purposefully make the lens not

parfocal by moving it away from the

focal plane a little bit so I used a

piece of wire as a shim and screwed the

lens in with this piece of wire here so

that it was out from the focal plane a

little ways and then magically this

property of being parfocal disappears

and even better than that with for doing

a dolly zoom there is a specific

distance that we can move this away from

the focal plane such that as we zoom in

and move the camera or farther away from

the subject everything stays in focus

for one given focal distance so thank

you if you set up the action at a

specific point in space the lens will

not be parfocal and as the camera drives

toward it everything will stay in focus

as you're changing

them all at the same time so here's a

look at the footage and it's pretty cool

you can see that the focus isn't perfect

but you can get an idea of what's going

on and I think it has potential I think

if there was like sparks or explosions

or water splashing and I was able to

move the camera even a little bit faster

I think this could be a pretty cool shot

okay I hope you enjoyed that see you

next time

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